There has recently been a demand for application that interconnects devices, such as a portable cellular phone terminal, an audiovisual device, a personal computer, and peripheral devices thereof, and that exchange data, such as multimedia information. Conceivable uses are; for instance, managing music data recorded by audio equipment through use of a personal computer and transferring video data recorded by visual equipment to a portable cellular phone terminal and viewing the thus-transferred video data outside.
Conceivable means for implementing such a demand is to connect the devices by means of a cable, to thus constitute a network. However, establishment of a wired network raises problems in terms of user's convenience, such as troublesome wire-connection work and restrictions on the layout of devices.
For these reasons, a wireless network has gained attention as means for enhancing convenience to a much greater extent. Practical use of techniques pertaining to a wireless LAN typified by IEEE802.11b and a wireless PAN (personal area network) typified by Bluetooth is proceeding.
Against such a backdrop, a communications scheme called an ultra-wide band (Ultra Wide Band hereinafter abbreviated as “UWB”) for transmitting a pulse-like modulation signal by use of a wide frequency band has received attention as a technique for inexpensively providing faster data communication.
The UWB is for enabling utilization of an extremely-wide frequency band and gaining a large capacity communications line by adoption of low transmission power of an order of magnitude which does not interfere with an existing radio system and yields an advantage of the ability to attain an extremely-high data transmission rate at nominal power. Some of wireless transmission schemes using the UWB use a technique for converting a pulse-like signal having broadband spectrum components into a radio frequency and transmitting the signal at the frequency.
When the wirelessly-transmitted pulse signal is received, processing in synchronism with the received pulse signal is required for reasons of demodulation. A receiver that enables performance of processing for demodulating the received pulse signal having a high transmission rate while assuring synchronization is a configuration; for instance, such as that described in Patent Document 1.
FIG. 15 shows a configuration for synchronization with a received pulse signal in the related art. Moreover, FIG. 16 illustrates a processing system 210 for demodulation purpose in addition to showing a sync processing system 215 shown in FIG. 15.
In FIG. 16, the received pulse signal input from an antenna 100 is mixed with a replica pulse internally generated by a demodulation correlation mixer 310 and sync correlation mixers 405 and 410 at different timings, whereby correlation values are determined. The correlation values are converted into digital values by means of the AD converters 220 and 225 and are subjected to processing for demodulation and sync control in a controller 230.
FIG. 17A shows a timing relationship between a received pulse signal and an internally-generated pulse that is to become a replica, and FIG. 17B shows a relationship between the two pulses in terms of a phase difference and a correlation output. The phase difference and the correlation output between the received pulse and the internally-generated pulse become symmetrical about a phase difference of zero and become maximum at the phase difference of zero.
FIGS. 18A to 18C show the phase difference and the correlation output obtained when synchronization is achieved. Two points designated by symbols T in the respective drawings are correlation values determined by the sync correlation mixers, and points designated by symbols A represent correlation values determined by the demodulation correlation mixers. As illustrated, it is possible to detect a state of synchronization with the received pulse in which correlation operation is performed by shifting at regular intervals the phase of the internally-generated pulse input to each of the correlation mixers.
FIG. 18A shows a state where optimum demodulation can be performed while synchronization is achieved, wherein a value output from the demodulation correlation mixer becomes maximum and two values output from the sync correlation mixers becomes equal to each other. FIGS. 18B and 18C show a state where synchronization is not achieved as a result of the received pulse and the internally-generated pulse being out of phase with each other in the demodulation correlation mixer. A difference arises in two output values from the sync correlation mixers.
The related-art device operates so as to change timing of the internally-generated pulse in such a way that the difference comes to zero by comparison of two correlation values of the sync correlation mixers 405 and 410 through use of an adder 415, to thus assure synchronization. As mentioned above, the invention described in Patent Document 1 enables receipt of wirelessly-transmitted pulse signals and demodulation of the signals while assuring synchronization by means of a configuration having in parallel a demodulation system using a correlator and a synchronization system.
Patent Document 1: JP-T-2005-518111 (FIG. 4, FIG. 5, FIG. 12A, FIG. 12B, and FIG. 14A to FIG. 14C)